Determining Gibbs Energies of Adsorption from Corrosion Inhibition Efficiencies: Is it a reliable approach?

The common practice of using inhibition efficiency (η%) to determine the standard
Gibbs energy of adsorption ( ΔGºads) for a corrosion inhibitor in acidic solution is
evaluated. It is demonstrated that the typical assumption that η% is a good proxy for fractional surface coverage (θ) is not necessarily valid. Consequently, the accuracy of the ΔGºads value obtained from such data is doubtful. Moreover, it is argued that even a more direct measurement of q may still not allow one to extract an accurate estimate of ΔGºads.